Ata

Geography & Climate

Ata is located in Japan, within the Ryukyu Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 31.22° N, 130.57° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. With a summit elevation of 924 meters above sea level, Ata is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a caldera, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Ata sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Japan near Ata, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Ata has 20 recorded eruptions in the geological database, spanning from 1450 BCE to 1615 CE. The most powerful recorded event was a cataclysmic eruption with ash columns reaching the stratosphere in 885 CE, reaching VEI 4 on the Volcanic Explosivity Index. Notable eruptions include 885 CE (VEI 4), 874 CE (VEI 4), 770 CE (VEI 4). With an average interval of roughly 153 years between eruptions over a span of 3,065 years, this is one of the more frequently active volcanoes in the database. This persistent activity suggests a robust and well-supplied magma system beneath the volcano.

Significance

With a maximum recorded VEI of 4, Ata has demonstrated the capacity for significant explosive eruptions that can impact regional aviation, agriculture, and communities tens of kilometers from the summit. VEI 4 eruptions produce ash columns reaching 15-25 kilometers into the atmosphere. Its 20 recorded eruptions make it one of the most prolific volcanoes in our database, reflecting a persistent and well-documented eruptive history that has provided volcanologists with extensive data for understanding eruption patterns and forecasting future activity.

GVP Reference Summary

The submerged 15 x 25 km Ata caldera under Kagoshima Bay is one of several large calderas in southern Kyushu and the source of major pyroclastic flows associated with its formation more than 40,000 years ago. The National Catalogue of the Active Volcanoes of Japan (JMA, 2013) included features of the Ibusuki field as part of the Ata post-caldera system. That area consists of numerous central cones and maars, the 4.5-km-wide Ikeda caldera, and Kaimondake stratovolcano. The symmetrical andesitic Kaimondake is the most prominent feature, and is capped by a lava dome. Ibusuki has been very active during the Holocene, forming the Ikeda caldera about 4,600 years ago, numerous maars and lava domes. Kaimondake formed during the last 4,000 years, from which all eruptive activity has occurred after about 2,650 years ago. Its last eruption took place in the 9th century. While listed as features of the Ata caldera, JMA (2013) simultaneously listed Kaimondake and the combination of Ikeda and Yamagawa as distinct volcanoes.

— Smithsonian Institution, Global Volcanism Program